Method of knock recognition

ABSTRACT

A method of knock recognition includes the introduction of evaluation factors, specific to the application, and the multiplication of the measured reference levels by these evaluation factors. These evaluation factors ensure that excessively high knock integrals of a particular cylinder, which is heard better than the other cylinders because of the sensor installation location, are not erroneously recognized as knocking.

BACKGROUND OF THE INVENTION

The present invention relates to a method of knock recognition. A methodof this type is already known. In this known method of knockrecognition, a common knock sensor on the engine block is associatedwith a four-cylinder engine of an internal combustion engine. This knocksensor records, for each cylinder, the noise level in the cylinderconcerned over a certain crankshaft angle. The knock sensor signalrecorded in this way is integrated over this crankshaft range. Thesignals which the knock sensor supplies are amplified for the individualcylinder. Because the different cylinders are heard with differentloudness levels by the knock sensor, because of its installationlocation, different reference levels result for the cylinders. Theamplification of the recorded reference level takes place with differentfactors on the basis of the different sound intensities. For anobjective comparison of the individual reference levels RP, astandardized reference level RPn is determined in which the referencelevel RP is divided by the amplification factor of the individualcylinder. These standardized reference levels in this way form the basisfor the knock recognition because measured knock integrals are analyzedwhich are referred to the reference level in normal operation, i.e. whenthe engine is running without knocking. In this known method, theaverage RPn of all the standardized reference levels RPn is firstformed. The quotient of the average RPn of all the cylinders and of thestandardized reference levels RPn of a cylinder determines the region ina knock recognition factor characteristic diagram from which a knockrecognition factor (K factor) is to be taken. This K factorcharacteristic diagram is arranged in terms of the standardizedreference level RPn and the rotational speed. The K factor (K)determined is multiplied by the reference level RP and, by this means,determines the knock threshold.

In this method, the selection of the K factor is erroneous because thesensor hears noises in a certain cylinder, which are actually normal, asbeing louder because of the installation location in the engine block.This means that the sensor emits a higher reference level for analysisin the case of a cylinder which can be heard easily. In consequence, thequotient of the standardized reference level of this cylinder and theaverage RPn is greater than that for the other cylinders. Because ofthis, the K factor is taken from a different region of thecharacteristic diagram so that the knock threshold for this cylinder isreduced. As a result, even a normal noise level can erroneously lead toknock recognition. In the reverse case, the knock threshold would beraised for a cylinder which is less easily heard because of anunfavourable sensor installation location and, in consequence, suppliessmaller knock integrals. Actual knocking in this cylinder would not,under certain circumstances, be recognized.

In addition, a method of knock recognition is known from EP 0 098 584 inwhich the knock signals filtered by means of a band pass are comparedwith a reference value by a comparator. If the knock signals are largerthan the reference value, a pulse is emitted by the comparator. Thesepulses are integrated and compared with a knock threshold fixed for thespecific cylinder. This knock threshold fixed for the specific cylinderis a direct decision criterion. This method does not permit the sensorsensitivity to be taken into account because the parameters individualto the cylinder are not already taken into account before the comparisonwith the reference level.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amethod of knock recognition, which avoids the disadvantages of the priorart.

In keeping with these objects and with others which will become apparenthereinafter, one feature of the present invention resides, brieflystated, in a method of knock recognition for internal combustion engineswith a plurality of cylinders, the numbers of knock sensors beingsmaller than the number of cylinders and knock recognition factors (Kfactors) for determined the knock threshold in a cylinder being calledup from a knock recognition factor characteristic diagram, which isarranged in terms of a standardized reference level and the rotationalspeed, in such a way that the quotient of the standardized referencelevel of a cylinder and the average of the standardized reference levelsof all cylinders determines the region in the knock recognition factorcharacteristic diagram from which the knock recognition factor is takenas a function of the rotational speed, wherein in accordance with thepresent invention the standardized reference level (RP/V) of eachcylinder is multiplied by an evaluation factor (f) before the selectionof the knock recognition factor, the evaluation factor (f) providingcompensation for the different reference levels which occur in normaloperation and are caused by the sensor installation location.

When the method is performed in accordance with the present invention,it has, in contrast, the advantage that, because of the association ofan evaluation factor with each cylinder for cylinders with different"loudness levels" which are caused by the sensor installation location,the knock recognition factor is taken from an average region for eachcylinder when the engine is not knocking.

It is particularly advantageous that it is possible to use an accuratelydefined region in the K factor characteristic diagram for each cylinderby calculating the average reference level in normal operation, when theengine is not knocking.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a K factor characteristic diagram and

FIG. 2 shows a block circuit diagram for the selection of the knockrecognition factor (K factor).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A knock recognition factor characteristic diagram is represented in FIG.1 and examples of values for the K factors of an internal combustionengine are entered in it. This characteristic diagram is arranged interms of the standardized reference level RPn and the rotational speedn. In the K factor characteristic diagram represented, the standardizedreference level RPn (in mV) is subdivided into individual regions A, B,C, D and E, the average RPn of all the standardized reference levelsbeing located in the region C. This means that in normal operation whenthe engine is not knocking, the region C is used for selecting the Kfactor and the K factor is now selected as a function of the rotationalspeed n. If the standardized reference level RPn of a cylinder deviatesfrom the average RPn, the K factor is taken from a different regiondepending on the nature of the deviation. This means that a cylinderwhich is heard "louder" makes use of another region (for example regionD) with a small K factor so that the knock threshold (K.RP) is reducedand, under certain circumstances, knocking is recognized, although thecauses of the larger standardized reference level lie in the arrangementof the sensor.

The essence of the invention is now explained with the aid of FIG. 2 andwhat has been stated above with respect to FIG. 1. The block circuitdiagram for the selection of the K factor is represented in FIG. 2 usinga 4-cylinder internal combustion engine as an example. A knock sensor 1records the noises in the individual cylinders, which are subsequentlyamplified for an individual cylinder (Vi) in an amplifier circuit 2. Therespectively recorded noise level of the knock sensor 1 is supplied tothe corresponding analysis circuit for this cylinder by appropriatelyclosing (for example by specifying with the ignition sequence) a switch3. The reference levels RP1 to RP4 for the specific cylinders are formedfrom the measured knock signal integrals by means of low-pass filtering4 and these reference levels are now present on the feed lines 5. In thesubsequent operational step, a standardized reference level RPn iscalculated in Stage 6 by dividing out the amplification factors V1 to V4of the individual cylinders. This is necessary because the amplificationfor the individual cylinders can be different, as is illustrated by thedifferent indices. As a result of this, the standardized referencelevels RPn4 to RPn4 of the individual cylinders are present on the feedlines 7. In the following operational step, each standardized referencelevel is multiplied by an individual cylinder evaluation factor f1 to f4in Stage 8. These evaluation factors f are already fixed in theapplication for each type of engine and they result from the fact thatthe reference levels formed by the knock integrals in Stage 4 can be ofdifferent magnitude, for the same noises, because of the sensorinstallation location. These evaluation factors f are fixed in such away that, in the case of an engine which is not knocking, the K factorfor each cylinder is taken from the region C of the K factorcharacteristic diagram. The further analysis now takes place in themanner already known from the prior art. This means that, in thefollowing operational step of Stage 9, the average RPn is calculated forall the standardized reference levels RPn multiplied by the respectivefactor f. in the subsequent operational step of Stage 10, the quotient Qof the standardized reference level and the average of all thestandardized reference levels is calculated for each cylinder. In thefurther operational step, one of the standard values A to E isrespectively associated, in a Stage 11, with the quotient Q which hasbeen determined, so that the corresponding region A to E to be used inthe K factor characteristic diagram is fixed in accordance with thevalue Q which has been determined. Using this K factor taken from thecharacteristic diagram region, the knock threshold of a cylinder isfinally calculated in Stage 12 and compared with the current referencelevel of the respective cylinder.

The analysis described is carried out during each combustion process sothat each stage is worked out with the current value. Particularly inthe case of the formation of the average RPn, the measured values forthe individual cylinders are deposited in a memory and used for theanalysis until a new measurement is present for this cylinder.

The evaluation factors f are determined in the application for thevarious engine types. For this purpose, the engine is operated in theregion where it does not knock and the reference levels of the differentcylinders supplied by a knock sensor are analysed in such a way that anevaluation factor is associated with each cylinder, said evaluationfactor ensuring that, in the case of operation without knocking, anaverage region of the knock factor characteristic diagram is used forall cylinders. These evaluation factors determined in this way arestored and, as a rule, remain for the life of the engine. It is,however, also possible to fix different evaluation factors for eachcylinder, referred for example to different load ranges.

Thus, the evaluation factors F are fixed for each of cylinders as afunction of different operational conditions of the internal combustionengine.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofmethods differing from the types described above.

While the invention has been illustrated and described as embodied in amethod of knock recognition for internal combustion engines, it is notintended to be limited to the details shown, since various modificationsand structural changes may be made without departing in any way from thespirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

What is claimed is:
 1. A method of knock recognition for internalcombustion engines with a plurality of cylinders, comprising the stepsof providing a number of knock sensors smaller than a number of thecylinders so that at least one of the cylinders is associated with eachof the knock sensors; determining for each of the cylinders a referencelevel by one of the knock sensors associated with each of the cylindersand said one of said knock sensors connected with an amplifier with anamplification factor; forming a standardized reference level for eachone of said cylinders by dividing the reference level for each of thecylinders by the amplification factor which is individual to each of thecylinders; multiplying the standardized reference level of each of saidcylinders by an evaluating factor which provides a compensation fordifferent reference levels occurring in a normal operation and caused byan installation location of each of said sensors; calculating an averagevalue of the standardized reference levels of all the cylindersmultiplied by the evaluation factors; determining a quotient of thestandardized reference level of each of the cylinders to the averagevalue of the standardized reference level of all the cylinders;determining from the quotient a region in a knock recognition factorcharacteristic diagram which covers the standardized reference level foreach of the cylinders and a rotational speed from which a knockrecognition factor is taken as a function of the rotational speed fordetermination of a knock threshold.
 2. A method as defined in claim 1,wherein the evaluation factor is determined as a function of theinstallation location for each of the cylinders of the internalcombustion engine.
 3. A method as defined in claim 1, wherein theevaluation factor for each of the cylinders is determined as a functionof the operational condition of the internal combustion engine.
 4. Amethod as defined in claim 1, wherein in a normal operation determiningthe knock recognition factor for each of the cylinders is taken in theregion of the knock recognition factor characteristic diagram which isassociated with the normal operation of the internal combustion engine.